Protein-protein interaction (PPI) network
To illustrate the interactions among the DEPs proteins, we carried out a PPI network analysis with all the DEPs at different Ca levels. A total of 28 proteins were matched to the PPI network (Figure 5, Supplementary Table S1). Node degree is a critical index to evaluate the importance and correlation of proteins in the PPI network. As shown in Figure 5 and Table S2, ten proteins with a degree over 6 were observed. The top 5 proteins according to their degrees were ranked as heat shock protein 70 (HSP70), enolase (LOS2), cytosolic ascorbate peroxidase (APX1), 2-Cys peroxiredoxin BAS1 (AT3G11630) and ATP synthase subunit beta (PB), suggesting their central roles in the interaction network. Multiple biological processes may be influenced by these central nodes.
A total of 4 highly enriched interaction function modules including photosynthesis, carbohydrate metabolism, oxidation stress response and chaperones were observed in the PPI network, suggesting exogenous Ca possibly mediated these physiological and metabolic processes in growingP. massoniana seedlings. The links among proteins belonging to different biological processes and pathways indicate there are potential crosslinks among Ca influenced diverse biological processes and metabolism pathways in P. massoniana seedlings.